2nd Monitor Window resize not working as expected

Help
1

On my openSUSE Tumbleweed (KDE/Plasma 5.27.4) I have to Monitors.
Main Monitor is an 32" UHD Monitor.
2nd Monitor is a 16" FullHD Minitor.
Use both as extended monitor setup (Ground Line adjusted) with X11 window manager.

If I shift a window to the 2nd Monitor and start to rescale them with the mouse on the button frame, it stops somewhere 1/5 above the ground line. It is not possible to extend the screen, only with the maximize button on the window (or with the middle mouse key to scale it top/button only).

Any idea about the root cause?

Should I create a bug report and if yes to kwin, X11 or …?

2

Video showing this problem I uplodaded to my PeerTube account
PeerTube-Video “KDE/Plasma 5.27.4 issue”

3

If I restart my PC, the apps started on the second small screen, are shifted a little bit up. So it must be always re-scaled and adjusted. I think this behavior have the same reason.

Remark: My Desktop you can see at: